GitHub does not allow users to archive repositories and the available plans have fixed limits for the amount of repositories one may have.

If I need to host more repositories than I'm allowed to and Some of those repositories are inactive, I would like to archive those repositories while keeping all the important information (issues, wiki, commits, ...). Then if I need to use one of those projects again, it would be good to have a way to activate that repository again.

Does anyone knows of a method or third party solution that allows me to achieve something similar to the above?

I work on different small projects that I would like to host on GitHub as private repositories. Those projects became inactive quickly but sometime I need to go back to one of them and fix a bug or do so changes.

Bitbucket is the way to go for lots of private repos, they only want you to pay when you need more collaborators on a project.
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AshfameDec 8 '12 at 13:05

Just a side note. Your comment is unfortunately outdated. Today (2014) Bitbucket is far, far before GitHub and using it for any kind of professional project management is a mistake. It has a lot of bugs and misses a lot of fundamental features, that GitHub has since initial build.
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trejderSep 21 '14 at 16:12

We had the same issue: many small inactive private repositories. There are some open source backup scripts/tools (like this one) but most of them are only for public repositories or can't restore properly. That is why we developed our own tool to archive our repositories and recently decided to offer it as a service backhub.co

You can simply login with your GitHub account and back up all repositories including issues, comments, milestones and wiki. It can also restore repositories back to GitHub incl. all the meta data. Restoring has some limitations though (due to GitHub API), all issues are submitted by you, not by the original user but we include the original information in the issue description. We also filter @mentions – otherwise collaborators might get a lot of mail notifications when restoring.